1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device for forming a via hole that is adopted to electrically connect an aluminum interconnect line to other layer.
2. Description of the Related Art
A via hole is generally employed to connect an interconnect line such as aluminum interconnect line in a semiconductor device to an electrode or the like of an element disposed in a different layer that contains the interconnect line (see, for example, JP-A-H10-32,248 (1998)). A conventional method for manufacturing a semiconductor device to form such a via hole is shown in FIG. 8. Process steps for forming a via hole are also shown in FIGS. 9 and 10. Descriptions thereof will be made as follows in reference to FIGS. 8 to 10.
First, as shown in FIG. 9A, a barrier metal layer (not shown) consisting of a titanium (Ti) film and a titanium nitride (TiN) film or a barrier metal layer consisting of only a TiN film is deposited on an SiOx layer 1 formed on a semiconductor substrate (not shown). Subsequently, an aluminum film, which will compose an aluminum interconnect line 2, is deposited on this barrier metal layer. A Ti film and a TiN film, which compose another barrier metal layer 3, are then deposited on the aluminum film in this order via a sputtering process (see FIG. 8, step 101). The sputtering process for depositing the aluminum film, which will compose an aluminum interconnect line 2, is conducted at a wafer temperature around 300 to 350 degree C. The sputtering process for depositing the Ti film composing the barrier metal layer 3 is carried out by utilizing remaining heat from the sputtering process for depositing the aluminum film. The wafer temperature in the sputtering process for the Ti film consequently becomes around 170 to 180 degree C. In FIGS. 9A to 9D and FIGS. 10E to 10G, only the barrier metal layer 3 formed on the aluminum interconnect line 2 is illustrated, and another barrier metal layer deposited between the aluminum interconnect line 2 and the SiOx layer 1 is not shown. Next, the TiN film, the aluminum film, the TiN film and the Ti film formed in this order are shaped into a predetermined pattern to form the barrier metal layer (not shown) between the aluminum interconnect line 2 and the SiOx layer 1, the aluminum interconnect line 2 and the barrier metal layer 3 (see FIG. 8, step 102). The film thickness of the TiN layer may be, for example, about 50 nm (500 angstrom), and the film thickness of the Ti layer may be, for example, about 15 to 25 nm (150 to 250 angstrom).
As shown in FIG. 9B, an inter-layer film 4 is then deposited on the SiOx layer 1 so as to cover the aluminum interconnect line 2 and the barrier metal layer 3 (FIG. 8, step 103).
Then, as shown in FIG. 9C, a photo resist (PR) 5 for forming a via hole is formed on the inter-layer film 4 (FIG. 8, step 104).
Then, as shown in FIG. 9D, a via hole 6 is formed by etching the inter-layer film 4 with the photo resist 5 (FIG. 8, step 105). Here, residues 7 generated in the etching process, which are residual matters of the photo resist, the Ti layer or the TiN layer, adhere onto the side walls or the like of the via hole 6 after the etching process is carried out.
Next, as shown in FIG. 10E, a plasma stripping processing is carried out to strip the photo resist 5 (FIG. 8, step 106).
Then, as shown in FIG. 10F, the residues 7 that adhere onto the side wall of the via hole 6 are removed by conducting an organic solvent-stripping processing with a chemical solution for cleaning the formed via hole 6 (FIG. 8, step 107). The organic solvent-stripping processing comprises three steps of: (1) wet-processing with a liquid chemical solution, (2) rinsing with a rinse liquid and (3) drying. Here, carbonated water, which is obtained by dissolving carbon dioxide (CO2) in pure water, is available for the rinse liquid.
Eventually, in order to remove TiOn (titanium oxide) exposing on the bottom of the via hole 6, which is a native oxide of TiN and is formed on the surface of TiN layer of the barrier metal layer 3, the TiN layer is partially eliminated via a radio frequency (RF) sputtering process such that about 10 nm (100 angstrom) in the entire thickness (about 50 nm (500 angstrom)) thereof is eliminated (see FIG. 10G, and FIG. 8, step 108).
Electric coupling of thus formed via hole 6 to the aluminum interconnect line 2 can be obtained by forming an electroconductive material in the via hole 6.
However, the contact resistance that is a resistance of a via often exceeds a criterion, when only a single via is formed corresponding to an aluminum interconnect line having larger area, or when a via hole is formed in the aluminum interconnect line, in which electric charge is structurally accumulated though the aluminum interconnect line does not have larger area. If the contact resistance exceeds the criterion, a failure occurs in the semiconductor device, thereby reducing the production yield.
The reason for increasing the contact resistance in the case of forming the via hole corresponding to the aluminum interconnect line having larger area will be described as follows in reference to FIG. 11.
As shown in FIG. 11, an anode oxidation is caused in the TiN layer of the barrier metal layer 3 disposed on the bottom of the via hole 6 when the aluminum interconnect line 2 is electrically charged, and thus the TiN layer is partially converting into TiO2. Then, a polycrystallization of TiO2 is occurred to create a cubical expansion within TiO2, thereby causing surface cracks on the surface of the barrier metal layer 3. As such, when surface cracks are occurred on the surface of the barrier metal layer 3, the contact area between the electrically conducting material formed in the via hole 6 and the barrier metal layer 3 is diminished, thereby increasing the contact resistance thereof.
It is described in “S .Gwo, C.-L. Yeh, P.-F. Chen, Y.-C. Chou, and T. T. Chen, T.-S. Chao, S.-F. Hu, and T.-Y. Huang, “Local electric-field-induced oxidation of titanium nitride films”, APPLIED PHYSICS LETTERS, 22 Feb. 1999, VOLUME 74, NUMBER 8, p.1090–1092” that the thickness of the above-mentioned TiN layer increases by increasing the applied bias voltage. A graph showing the relationship between the thickness of the TiN layer (Height) and the applied bias voltage (Sample Bias) disclosed in the above letter is shown in FIG. 12. As can be seen from the graph shown in FIG. 12, it is found that higher voltage or potential of the accumulated charge within the aluminum interconnect line provides thicker film thickness of the TiN layer via an anodization of TiN.
The aforementioned conventional methods for manufacturing the semiconductor devices involve a problem, in which the electric charge accumulated in the aluminum interconnect line during the formation process of the via hole for coupling to the aluminum interconnect line may cause an increase of the contact resistance thereof such that the manufactured products may be defective products, thereby decreasing the production yield of the semiconductor devices.